1. Field of the Invention
The present invention relates to a rotational drive device that rotatingly drives a rotated body. In particular, the present invention relates to the improvement of a rotational drive device, of an aspect where a drive motor and a drive transmission mechanism are coupled together via an input coupling, and various processing devices, such as image forming devices, using the rotational drive device.
2. Description of the Related Art
Conventionally, in rotational drive devices that rotatingly drive a rotated body, a system has been widely used where the driving force from a drive motor is directly transmitted to the rotated body or is damped down with a drive transmission mechanism and then it is transmitted to the rotated body (e.g., see Patent Documents 1 to 3).
In this type of rotational drive device, in a case where, for example, a planetary speed-reducing mechanism (planetary roll speed-reducing mechanism, planetary gear speed-reducing mechanism) is used as the drive transmission mechanism, it is necessary to coaxially couple the rotating shaft of the rotated body with the drive shaft of the drive motor via the planetary speed-reducing mechanism (e.g., see Patent Documents 1 and 3), and the axial-direction length ends up being long in comparison to an aspect where a non-coaxial type speed-reducing mechanism resulting from an ordinary gear train (aspect where the rotating shaft of the rotated body and the drive shaft of the drive motor are not coaxially disposed) is used.
Moreover, in a case where a stepping motor is used as the drive motor, it becomes easy for vibration generated by the stepping motor itself to result in unevenness in the rotation of the rotated body. Thus, a method where a flywheel or a dynamic damper is attached to the side of the drive motor opposite from the output shaft and a method where a flywheel is attached to one end of the rotating shaft of the rotated body (e.g., see Patent Documents 4 and 5) have been used from the standpoint of increasing the moment of inertia of the rotor and reducing uneven rotation of the motor itself.
Patent Document 1: JP-A-4-155352 (“Configuration” and FIG. 2)
Patent Document 2: JP-A-10-333387 (“Embodiments of the Invention” and FIG. 1)
Patent Document 3: JP-A-2002-78289 (“Embodiments of the Invention” and FIG. 1)
Patent Document 4: JP-A-2001-188438 (“Embodiments of the Invention” and FIG. 1)
Patent Document 5: JP-A-10-4476 (“Embodiments of the Invention” and FIG. 1)
Patent Document 6: JP-A-2002-171721 (“Embodiments of the Invention” and FIG. 2)
In the rotational drive devices of Patent Documents 1 and 2, a configuration is ordinarily used where, as shown for example in FIGS. 21 and 22, a drive motor 510 and a drive transmission mechanism 520 are coaxially coupled together via an input coupling 530. Thus, a situation where the axial-direction length of the rotational drive device increases cannot be avoided in comparison to an aspect using a non-coaxial type drive transmission mechanism, and there is a demand to shorten as much as possible the axial-direction length of the rotational drive device. It should be noted that, in FIG. 21, reference numeral 511 represents a housing of the drive motor 510, reference numeral 521 represents a housing of the drive transmission mechanism 520, and both housings 511 and 521 are fixed with fasteners such as screws. Also, the housing 521 of the drive transmission mechanism 520 is omitted from FIG. 22.
The input coupling 530 used here has the role of absorbing the slight oscillating movement of the shaft, which is generated by the straightness error of the shaft of the drive motor 510 and squareness error with the attachment surface, and transmitting rotational motion to the drive transmission mechanism 520. When an output shaft 512 of the drive motor 510 and the drive transmission mechanism 520 are directly coupled together without intervening the input coupling 530, as in Patent Document 3, the drive transmission mechanism 520 directly receives the oscillating movement of the drive motor 510 shaft and it becomes easy for large load torque fluctuations to arise. Also, there are many cases where the material characteristics respectively demanded of the output shaft 512 of the drive motor 510 and the drive transmission mechanism 520 are different, and in these cases also it is effective to couple the output shaft 512 of the drive motor 510 and the drive transmission mechanism 520 via the input coupling 530.
Additionally, as mentioned above, in an aspect using a stepping motor as the drive motor 510, as shown in FIGS. 20 and 21, a flywheel 540 must be disposed at the side of the drive motor 510 opposite from the output shaft 512, or a flywheel must be disposed at one end of the rotating shaft of the rotated body, in order to prevent the transmission of vibration from the drive motor 510. Thus, with respect to the axial-direction length of the rotational drive device and the rotated body, consideration must be given to the space in which the flywheel is disposed and, as a result, a situation where the axial-direction length of the rotational drive device and the rotated body further increases cannot be avoided.
In order to solve this technical problem, in a photosensitive drum drive where it is desirable for rotational vibration to be prevented, it is common to use an outer rotor type DC brushless motor for the drive motor of the rotational drive device so that a flywheel effect is imparted to the rotor of the motor (e.g., see Patent Document 6). However, in this case, it becomes impossible to finely adjust the rotational speed of the drive motor due to the affect of the flywheel effect. That is, both the angle error and speed unevenness of the drive motor cannot be simultaneously made small. In, for example, a tandem color printer, this leads to not being able to respond to the demand to synchronize, with high precision, plural photosensitive drums and eliminate image stripes (banding) resulting from rotational unevenness in order to raise color stability like printing.